Thermal processing apparatus and a thermal processing method

ABSTRACT

Substrates having surfaces in a highly clean condition are subjected to a thermal process in a heating furnace. In a thermal processing apparatus for processing substrates by a predetermined thermal process that heats the substrates by a heating means, the substrates are held in a vertical position at horizontal intervals in a reaction vessel. Cleaning liquids are supplied into the reaction vessel to clean the substrates, and then the cleaning liquids are drained away through a drain port, and then a process gas is supplied into the reaction vessel to process the substrates by a thermal process. The substrates having the cleaned clean surfaces are subjected to the thermal process without being exposed to the ambient atmosphere and can be satisfactorily processed by the thermal process.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a thermal processing apparatus and a thermal processing method for processing substrates, such as semiconductor wafers, by a thermal process, such as a CVD process.

2. Description of the Related Art

A vertical thermal processing apparatus processes semiconductor wafers (hereinafter referred to simply as “wafers”) in lots by a batch thermal process, such as a batch CVD process (batch chemical vapor deposition process) for depositing a film on wafers, a batch oxidation process or a batch diffusion process. This thermal processing apparatus includes a heating furnace provided with a vertical reaction tube having an open lower end. A wafer boat holding a plurality wafers in a stack is mounted on a lid for closing the open lower end of the reaction tube, the wafer boat is loaded into the reaction tube by raising the lid, and processes the wafers by a predetermined thermal process.

A wafer carrier holding wafers is delivered to process stations in a factory or to a stocker. Wafers held in the wafer carrier are contaminated with particles and organic matters and are oxidized by natural oxidation by the oxidizing effect of the atmosphere while the wafer carrier is transported. Therefore, it is a usual procedure to clean wafers by a cleaning apparatus by successive cleaning processes using some chemical solutions including a hydrofluoric acid solution, to put the cleaned wafers in a wafer carrier, and the wafer carrier is carried to the thermal processing apparatus.

When the cleaning apparatus is installed in an area separated from an area in which the thermal processing apparatus is installed, the cleaned wafers are exposed to the atmosphere and undergo natural oxidation after cleaning, and an oxide film is formed on the wafers before the wafers are loaded into the reaction vessel of the thermal processing apparatus. The adverse effect of even a little oxide film formed by natural oxidation on the characteristics of devices becomes more serious as the thickness of thin films forming devices decreases progressively. Either organic or inorganic impurities affect the characteristics of devices adversely. For example, there is a tendency for the desired thickness of a silicon oxide film as a gate oxide film for CMOS devices to decrease to thicknesses below 10 nm. Under such circumstances, it is required to reduce the amount of impurities carried into the reaction vessel to the least possible extent; that is it is required to keep the surfaces of wafers as clean as possible.

FIGS. 8(a) and 8(b) show a thermal processing apparatus such as proposed in Patent document 1 to meet such a requirement. This prior art thermal processing apparatus has a wafer carrier handling block B1 for receiving and sending out wafer carriers holding wafers, a cleaning chamber B2 in which wafers taken out of the wafer carrier are cleaned, and a film forming chamber B3 in which a film is formed on the cleaned wafers. A wafer boat 11 for holding wafers W in a stack is placed in the cleaning chamber B2, wafers W are transferred successively from a wafer carrier to the wafer boat 11, the cleaning chamber B2 is sealed hermetically, and then a chemical solution is jetted through vertically arranged nozzles 12 onto the wafers W. Then, pure water is jetted through other nozzles 12 onto the wafers W, IPA (isopropyl alcohol) is jetted through nozzles onto the wafers W, and the wafer boat 11 is rotated by a motor M to remove water drops remaining on the wafers W by centrifugal force. Subsequently, the cleaning chamber B2 is filled up with nitrogen gas, and then the wafer boat 11 is transferred to an elevator disposed below the film forming chamber B3.

Patent document 1: JP-A 8-203852 (Paragraph 0028, II. 7 to 9, FIGS. 1, 7 and 9).

When the wafers W are processed by this prior art thermal processing apparatus, the wafer W is exposed to the ambient atmosphere while the cleaned wafers W are transferred from the cleaning chamber B2 to the film forming chamber B3. Consequently, for example, an oxide film is formed on the surface of the wafers W by natural oxidation or impurities floating in the ambient atmosphere, such as organic substances including hydrocarbons, and moisture, adhere to the surfaces of the wafers W. If the wafers W thus contaminated are subjected to, for example, a thermal process for forming a silicon dioxide film, parts of a film corresponding to the oxide film formed by natural oxidation are formed in a thickness greater than that of other parts, a film having an irregular thickness is formed, and it is possible that a low-quality silicon dioxide film containing impurities is formed and such a low-quality silicon dioxide film affects the characteristics of devices formed on the wafers W adversely.

Since the thermal processing apparatus has the cleaning chamber specially for the cleaning process and needs a wafer boat handling mechanism, the thermal processing apparatus is inevitably large and needs a large space for installation. There is a tendency for the vertical thermal processing apparatus to use a reaction vessel having a low height and capable of batch-processing an increased number of wafers. Consequently, the pitches of wafers on a wafer boat are progressively decreased. When the cleaning liquid is jetted through the nozzles as mentioned in connection with FIG. 8(b), the cleaning liquid cannot be satisfactorily jetted onto the surfaces of the wafers arranged at short pitches. Consequently, the wafers cannot be satisfactorily cleaned and it is possible that the oxide film formed by natural oxidation remains on the surface of the cleaned wafers.

SUMMARY OF THE INVENTION

The present invention has been made in view of those problems and it is therefore an object of the present invention to provide a thermal processing apparatus and a thermal processing method capable of keeping the surfaces of substrates in a highly clean condition in processing the substrates by a thermal process in a heating furnace.

A thermal processing apparatus in a first aspect of the present invention for processing substrates by a predetermined thermal process that heats the substrates by a heating means includes: a reaction vessel provided with a drain port; a cleaning liquid supply means for supplying cleaning liquids into the reaction vessel to clean the substrates after the substrates have been loaded into the reaction vessel; and a process gas supply means for supplying a process gas into the reaction vessel to process the substrates by the thermal process after the cleaning liquids have been drained away from the reaction vessel.

A thermal processing apparatus in a second aspect of the present invention for processing substrates by a predetermined thermal process that heats the substrates by an external heating means includes: a reaction vessel provided with a drain port; a lid for closing an inlet opening of the reaction vessel; a substrate holding device mounted on the lid to hold the substrates; a carrying means for carrying the substrate holding device into and carrying the same out from the processing vessel; a cleaning liquid supply means for supplying cleaning liquids into the reaction vessel to clean the substrates after the substrate holding device holding the substrates has been loaded into the reaction vessel; and a process gas supply means for supplying a process gas into the reaction vessel to process the substrates by the thermal process after the cleaning liquids have been drained away through the drain port.

The substrate holding device may hold a plurality of substrates in a vertical position at horizontal intervals. The cleaning liquid supply means may be connected to the lid and/or the drain port may be formed in the lid. The cleaning liquid supply means may be used for filling up the reaction vessel with the cleaning liquid, and the drain port may be closed while the cleaning liquid is supplied into the reaction vessel.

A thermal processing method in a third aspect of the present invention includes the steps of: carrying substrates into a reaction vessel; cleaning the substrates by supplying cleaning liquids into the reaction vessel; draining away the cleaning liquids from the reaction vessel; processing the substrates by a thermal process by supplying process gases into the reaction vessel and heating the interior of the reaction vessel after the cleaning liquids have been drained away.

A thermal processing method in a fourth aspect of the present invention that processes substrates by a predetermined thermal process in a reaction vessel by heating the substrates with an external heating means includes the steps of: loading a substrate holding device with the substrates; loading the substrate holding device into the reaction vessel and hermetically closing an loading opening of the reaction vessel by a lid; cleaning the substrate by supplying cleaning liquids into the reaction vessel; draining away the cleaning liquids from the reaction vessel; and processing the substrates by the thermal process by supplying a process gas into the reaction vessel and heating the interior of the reaction vessel.

The step of loading the substrate holding device with the substrates may load the substrates onto the substrate holding device such that the substrates are held in a vertical position at horizontal intervals. The cleaning liquids may be supplied through a discharge port formed in the lid into the reaction vessel. The cleaning liquids may be drained away through a drain port formed in the lid. The step of supplying the cleaning liquids into the reaction vessel may fill up the reaction vessel with the cleaning liquid.

The thermal processing apparatus of the present invention processes the substrates in the reaction vessel by the thermal process after cleaning the substrates with the cleaning liquids in the reaction vessel. Thus, the cleaned substrates are not exposed to the ambient atmosphere, the substrate having the clean surfaces cleaned by the cleaning process can be subjected to the thermal process. Consequently, the substrates can be satisfactorily processed by the thermal process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a thermal processing apparatus in a preferred embodiment according to the present invention;

FIG. 2 is a longitudinal sectional view of the thermal processing apparatus embodying the present invention;

FIG. 3 is a longitudinal sectional view of a heating furnace included in the thermal processing apparatus;

FIG. 4 is a plan view of the heating furnace of the thermal processing apparatus;

FIG. 5 is a perspective view of a substrate holding device included in the heating furnace;

FIG. 6 is a perspective view of a position changing device included in the thermal processing apparatus;

FIG. 7 is a view of assistance in explaining a method of supplying a cleaning liquid into a reaction vessel included in the thermal processing apparatus; and

FIG. 8 is a view of assistance in explaining a prior art thermal processing apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The general configuration of a thermal processing apparatus in a preferred embodiment according to the present invention will be described with reference to FIGS. 1 and 2 prior to the description of the thermal processing apparatus. The thermal processing apparatus has a transfer port A1 for receiving and sending out a wafer carrier C holding, for example, fifteen wafers W, namely, substrates, in a stack, and a loading area A2 where wafers W are loaded into a heating furnace for carrying out a thermal process to subject the wafers W to the thermal process. The transfer port A1 and the loading area A2 are separated by a partition wall 20 so as to isolate the spaces in the transfer port A1 and the loading area A2 from each other.

Installed in the transfer port A1 are a first table 21 for supporting a wafer carrier C received from an external apparatus, a second table 22 for supporting a wafer carrier C while wafers W contained in the wafer carrier C are carried into the loading area A2, and a carrier carrying mechanism 23 for carrying a wafer carrier C between the tables 21 and 22. The wafer carrier C is provided with a lid. The wafer carrier C is sealed hermetically to prevent exposing the wafers W held therein to the atmosphere when the wafers W are carried from the preceding process to the thermal process and from the thermal process to the succeeding process. A lid operating mechanism combined with a door 24 closing an opening formed in the partition wall 20 removes the lid to expose the interior of the wafer carrier C to an atmosphere in the loading area A2.

A side flow of clean air is produced in the loading area A2. Installed in the loading area A2 are a first carrying device 3 and a second carrying device 4 for carrying a wafer W along predetermined paths, respectively, a heating furnace 5 in which wafers W are subjected to the thermal process, and a position changing deice 6 for changing the position of a wafer between a horizontal position and a vertical position.

The first carrying device 3 has a carrier base 32, an arm unit 31 including a plurality of arms arranged at predetermined vertical intervals and supported on the carrier base 32 so as to be horizontally movable to support a peripheral part of each of wafers W from below the wafer, and a driving system 33 for moving the carrier base 32 horizontally, i.e., in directions along the width of the thermal processing apparatus, moving the carrier base 32 vertically and turning the carrier base 32 about a vertical axis. The first carrying device 3 carries wafers W between a wafer carrier C and a position changing device 6.

The second carrying device 4 has a carrier base 42, an arm unit 41 including a plurality of longitudinally arranged pairs of arms supported for longitudinal movement on the carrier base 42 to support wafers W set in a vertical position by the position changing device 6 by their peripheral parts, i.e., parts outside their device forming regions, and a driving system 43 for moving the carrier base 42 horizontally, i.e., in directions along the width of the thermal processing apparatus, and moving the carrier base 42 vertically. The second carrying device 4 carries wafers W between the position changing device 6 and the heating furnace 5.

The heating furnace 5 will be described with reference to FIGS. 3 and 4. Referring to FIGS. 4 and 5, a reaction vessel 51 is placed in a furnace body 50. The reaction vessel 51 has, for example, a cylindrical shape, is formed of a nonmetallic material, such as quartz or a ceramic material, and defines a heating space in which wafers W are placed for the thermal process. The reaction vessel 51 has an open lower end 53 defining an opening through which wafers W are carried into and out of the reaction vessel 51. A lid 7 is disposed under the open lower end 53. The lid 7 is vertically movable to close and open the open lower end 53 of the reaction vessel 51. At least the surface of the lid d7 is formed of a nonmetallic material, such as quartz or a ceramic material. A wafer boat 71 is supported by a shaft 72 on the lid 7. The wafer boat 71 is capable of holding a plurality of wafers W, for example, twenty-five to fifty wafers W, in a vertical position in s horizontal arrangement. The lid 7 is raised by a boat elevator 73 included in an elevator unit to load wafers W held on the wafer boat 71 into the reaction vessel 51 and to close the open lower end 53 of the reaction vessel 51 so as to seal the reaction vessel 51 hermetically. A flange 51 a is formed on the lower end of the reaction vessel 51, and an O ring 51 b, i.e., a sealing member formed of a resin, is placed on the lid 7. When the lid 7 supporting the wafer boat 71 is raised and brought into contact with the flange 51 a, the gap between the lid 7 and the open lower end 53 is sealed hermetically by the O ring 51 b.

More specifically, as shown in FIG. 5, the wafer boat 71 includes a horizontal plate 74, a pair of vertical end plates 75 set on the horizontal plate 74 so as to be opposed to each other, for example, three support rods 76, i.e., substrate support members, are extended between the opposite end plates 75. The support rods 76 are provided with grooves 76 a formed at longitudinal intervals. The second carrying device 4 brings wafers W from above the wafer boat 71 and inserts peripheral parts of the wafers W in the grooves 76 a to hold the wafers W by the wafer boat 71. If necessary, the horizontal plate 74 and the end plates 75 may be provided with openings 77 to enable process gases and cleaning liquids to flow across the horizontal plate 74 and the end plates 75. The openings 77 enable the process gases or the cleaning liquids to flow smoothly when wafers W are processed. Consequently, the process gases and the cleaning liquids can be uniformly supplied into spaces between the wafers W.

Referring to FIGS. 3 and 4 again, a heater 54, such as a carbon wire heater, i.e., heating means, is disposed, for example, in a space between the furnace body 50 and the reaction vessel 51. A carbon wire heater is preferable because the carbon wire heater is capable of heating a process atmosphere in the reaction vessel 51 at a high heating rate of, for example, 100° C./min. The carbon wire heater may be such a heater formed by sealing a carbon wire formed by twisting a plurality of carbon fiber strands in a ceramic case, such as a transparent quartz tube having an outside diameter of ten-odd millimeters. The carbon wire heater is formed vertically inside the furnace body 50. The heating element of the heater is not limited to the carbon wire and may be a metal wire, such as an iron/nickel/chromium alloy wire.

A process gas supply pipe 8, i.e., process gas supply means, is connected to a lower part of the side wall of the reaction vessel 51 so as to open downward. The process gas supply pipe 8 is connected by a gas supply line 81, such as gas supply pipes, to process gas sources, i.e., an oxygen source 82 and a steam source 83 in this embodiment. Indicated at V1 to V3 are valves (gas supply valves. Nitrogen gas supply pipes 84 for carrying dry nitrogen gas, i.e., inert gas supply pipes for carrying a dry inert gas, are connected to a lower part of the side wall of the reaction vessel 51. The nitrogen gas supply pipes 84 rise from a lower part to a middle part of the interior of the reaction vessel 51, and extend horizontally along the direction of arrangement of the wafers W held on the wafer boat 71 respectively on the opposite sides of the arrangement of the wafers W. Outer ends of the nitrogen gas supply pipes 84 are connected to a valve V4 connected to a nitrogen gas source 85. The nitrogen gas supply pipes 84 are provided with blowing holes 84 a. Nitrogen gas is blown through the blowing holes 84 a against the wafers W held on the wafer boat 71 after cleaning the wafers W with cleaning liquids to dry the wafers W. A plurality of nitrogen gas supply pipes 84 may be arranged vertically in a range corresponding to the height of the wafers W. When the nitrogen gas supply pipes 84 are arranged so, nitrogen gas can be more surely blown against the surfaces of the wafers W. The nitrogen gas supply pipes 84 may be vertically movable. A discharge line 86, such as a discharge pipe, is connected to a discharge port 52 formed in an upper part of the reaction vessel 51. The discharge line 86 is connected to a valve V5 connected to a discharge device 87 to discharge gases contained in the reaction vessel 51 from the reaction vessel 51 by the discharge device 87. A branch line 84 a branched from the nitrogen gas supply line 84 is connected through a valve V6 to the discharge line 86. The valve V5 is closed and the valve V6 is opened to supply nitrogen gas from an upper part of the reaction vessel 51 into the reaction vessel 51.

A cleaning liquid supply nozzle 9, namely, a cleaning liquid supply means, is set, for example, vertically so as to project from the upper surface of the lid 7. The cleaning liquid supply nozzle 9 is connected to a hydrofluoric acid solution source 92, a pure water source 93 and an IPA (isopropyl alcohol) source 94 by a cleaning liquid supply line 91, such as a cleaning liquid supply pipe, extended in the boar elevator 73. The hydrofluoric acid solution source 92 supplies, for example, a 10% by weight hydrofluoric acid solution. Indicated at V7 to V9 are valves (cleaning liquid supply valves), and P1 to P3 are pumps. The lid 7 is provided with a drain port 95. The drain port 95 is connected to a drain tank, not shown, by a drain line 96, namely, drain pipe. A valve V10 (drain valve) is placed in the drain line 96 to open and close the drain port 95.

The position changing device 6 for changing the position of wafers W mentioned in connection with FIGS. 1 and 2 will be described with reference to FIG. 6. A swivel box 61 has an open front side. Support rails 62 for supporting wafers W thereon are arranged vertically at intervals corresponding to the thickness of the wafers W on the inner surfaces of the side walls of the swivel box 61. The wafers W are inserted in spaces between the support rails 62 so as to be supported on the support rails 62 in the swivel box 61. A horizontal shaft 64 is attached to lower back parts of the side walls of the swivel box 61. The shaft 64 has a base end connected to a turning mechanism 65. The turning mechanism 65 turns the shaft 64 in opposite directions through 900 about a horizontal axis to swivel the swivel box 61 forward and backward so that the wafers W contained in the swivel box 61 are turned between a horizontal position and a vertical position.

The swivel box 61 has an open back side 61 a. A lifting device 66 provided with a lifting table 67 is disposed such that the lifting table 67 is opposite to the open back side 61 a of the swivel box 61 when the swivel box 61 is set in a horizontal position in which the wafers W held in the swivel box 61 are set in a vertical position. The lifting table 67 moves through the open back side 61 a into the swivel box 61 when the lifting table 67 of the lifting device 66 is raised. As shown in FIG. 6(b), the lifting table 67 is provided in its upper surface with grooves 67 a for receiving peripheral parts of the wafers W. The edges of the grooves 67 a are chamfered. The lifting table 67 is connected by a shaft 69 to a lifting mechanism 68. The lifting mechanism 68 raises the lifting table 67 to lift up the wafers W contained in the swivel box 61. Then, the second carrying device 4 holds the lifted wafers W to receive the wafers W from the lifting table 67. Thus the wafers W can be transferred from the lifting device 66 to the second carrying device 66 and vice versa.

The thermal process for processing wafers W by the thermal processing apparatus will be described. An oxidation process, as a thermal process, for forming a silicon dioxide film on surfaces of wafers W will be described by way of example. Referring to FIGS. 1 and 2, a waver carrier C is delivered to the first table 21 of the transfer port A1 by an automatic carrying robot. The carrier carrying mechanism 23 carries the wafer carrier C to, for example, a carrier storage unit, not shown, for temporary storage. The carrier carrying mechanism 23 carries the wafer carrier C from the carrier storage unit to the second table 22. The lid of the wafer carrier C is removed after the wafer carrier C has been pressed against the partition wall 20, and then the door 24 is opened.

Subsequently, the arm unit 31 of the first carrying device 3 advances into the wafer carrier C, takes out a plurality wafers W, for example, five wafers W, simultaneously from the wafer carrier C and carries the wafers W into the swivel box 61 set in a vertical position. The arm unit 31 repeats this operation to transfer all the wafers W contained in the wafer carrier C to the swivel box 61. Then, the turning mechanism 65 turns the shaft 64 to swivel the swivel box 61 through 90° to set the wafers W held in the swivel box 61 in a vertical position. Then, the arm unit 41 of the second carrying device 4 is moved to a position above the swivel box 61, holds all the wafers W, for example, fifteen wafers W, lifted up from the swivel box 61 by the lifting device 66, and carries the wafers W to loads the same on the wafer boat 71. The arm unit 41 repeats this operation to load the wafer boat 71 with a predetermined number of wafers W. After the wafer boat 71 has been thus fully loaded with the wafers W, the second carrying device 4 is retracted.

Subsequently, the boat elevator 73 is raised to load the wafer boat 71 holding the wafers W into the reaction vessel 51, and the open lower end 53 of the reaction vessel 51 is closed by lid 7 to seal the reaction vessel 51 hermetically. Then, the valves V5 and V7 are opened, and the hydrofluoric acid solution, namely, a cleaning liquid, is supplied through the cleaning liquid supply nozzle 9 into the reaction vessel 51 to fill up the reaction vessel 51 with the hydrofluoric acid solution as shown in FIG. 7(a). Then, the hydrofluoric acid solution contained in the reaction vessel 51 is heated by the heater 54 at a temperature, such as 80° C., at which the hydrofluoric acid solution will not boil and interaction between the hydrofluoric acid solution and oxide films formed by natural oxidation on the wafers W is promoted. A state where the reaction vessel 51 is filled up with the cleaning liquid is a state where the level of the cleaning liquid is higher than that of the upper ends of the wafers W. The oxide films formed by natural oxidation on the surfaces of the wafers W and impurities adhering to the surfaces of the wafers W can be removed by immersing the wafers W in the hydrofluoric acid solution for a predetermined time. Then, the valves V7 and V5 are closed, and the valves V6 and V10 are opened to drain the hydrofluoric acid solution from the reaction vessel 51 and to supply nitrogen gas into the reaction vessel 51. After the hydrofluoric acid solution has been completely drained away, the valves V6 and V10 are closed, and the valves V8 and V5 are opened to fill up the reaction vessel 51 with pure water, namely, cleaning liquid, by supplying pure water through the cleaning liquid supply nozzle 9 into the reaction vessel 51. Thus the hydrofluoric acid solution remaining on the wafers W is rinsed away. Then, the valves V8 and V5 are closed and the valves V6 and V10 are opened to drain the pure water from the reaction vessel 51. Then, the valves V6 and V10 are closed, and the valves V5 and V9 are opened to fill up the reaction vessel 51 with IPA, namely, cleaning liquid, by supplying IPA trough the cleaning liquid supply nozzle 9 into the reaction vessel 51. Then, the valves V9 and V5 are closed, and the valves V6 and V10 are opened to drain the IPA away from the reaction vessel 51. The IPA reduces the surface tension of water droplets (droplets of the pure water) adhering to the surfaces of the wafers W. Consequently, the water droplets flow along the surfaces of the wafers W held in a vertical position and drop away from the wafers W.

The valves V5 to V10 are opened and closed on the basis of a sequence program stored in a controller, not shown, to supply hydrofluoric acid solution, pure water and IPA sequentially into the reaction vessel 51 and to supply and to stop supplying nitrogen gas into the reaction vessel 51 for the cleaning process. The valves V1 to V3 and V5 may be opened and closed to supply and to stop supplying the process gases and a purge gas for the thermal process, which will be described later, on the basis of a sequence program stored in the controller. IPA may be supplied in either a liquid or a vapor. An IPA vapor supply line may be connected to the lid 7 when IPA is supplied in a vapor.

Then, the valve V5 is opened, the valves V6 to V9 are closed, and the valve V4 is opened to supply nitrogen gas, namely, a dry gas, through the nitrogen gas supply pipes 84 into the reaction vessel 51 for a drying operation. As mentioned above, the nitrogen gas supply pipes 84 are provided with the blowing holes 84 a corresponding to the wafers W. Nitrogen gas is blown against the wafers W to dry the wafers W quickly and to purge the reaction vessel 51 with the nitrogen gas. After the drying operation has been continued for a predetermined time, the valve V4 is closed to stop supplying nitrogen gas. The valve V5 in the discharge line 86 is kept open while nitrogen gas is supplied into the reaction vessel 51 and is closed when nitrogen gas supply is stopped.

Then, the interior of the reaction vessel 51 is heated by the heater 54 at a process temperature of, for example, 1000° C.

A process gas, a mixed gas containing, for example, oxygen gas and steam, is supplied through the gas supply pipe and the process gas supply pipe 8 into the reaction vessel, while the discharge device 87 discharges gases contained in the reaction vessel 51 from the reaction vessel 51 so as to keep the atmosphere in the reaction vessel 51 at a predetermined pressure, such as a slightly reduced pressure. Silicon in the surface layers of the wafers W is oxidized to form silicon diocese films on the wafers W, respectively, by the thermal process.

After continuing the thermal process for a predetermined time, the valves V1 to V3 are closed to stop supplying the process gas. The valve V4 is closed after purging the reaction vessel 51 with nitrogen gas, the boat elevator 73 is lowered to a predetermined lower position, and the lid 7 is opened to release the reaction vessel 51 from an airtight state. Then, the wafer boat 71 holding the wafers W is unloaded from the reaction vessel 51. Then the foregoing operation for transferring the wafers W from the wafer carrier C to the wafer boat 71 is reversed to return the wafers W to the wafer carrier C; that is, the second carrying deice 4 receives the wafers W from the wafer boat 71 and carries the wafers W into the swivel box 61, the swivel box 61 is turned forward to set the swivel box 61 in a vertical position so that the wafers W are held in a horizontal position in the swivel box 61, and then the first carrying device 3 transfers the wafers W from the swivel box 61 to the wafer carrier C. Thus the thermal process is accomplished.

The thermal processing apparatus in this embodiment cleans the wafers W by supplying the cleaning liquids into the heating furnace 5 by the cleaning liquid supply system, and supplies the process gas into the heating furnace 5 to process the wafers W by the thermal process. Therefore, the cleaned wafers W are not exposed to the ambient atmosphere and silicon dioxide films can be formed on the clean surfaces of the cleaned wafers W by the thermal process. Therefore, the silicon dioxide films formed on the surfaces of the wafers by the thermal process are of very high quality not containing any oxide film formed by natural oxidation at all or scarcely containing such an oxide film. Consequently, high-quality thin gate oxide films can be formed and satisfactory semiconductor devices can be fabricated on those wafers W. Nitrogen gas supplied into the reaction vessel 51 works for both drying the cleaned wafers W and purging the reaction vessel 51 to keep the surfaces of the wafers W clean. Therefore, the thermal processing apparatus is simple in construction and is able to operate at a low operation cost because a nitrogen gas atmosphere does not need to be created in the loading area A2.

Although the oxidation process has been described by way of example, the thermal processing apparatus may be used for carrying out a CVD process. If films deposited on the inner surfaces of the reaction vessel 51 and the surfaces of the wafer boat 71 and the lid 7 during the CVD process are those of substances that can be removed by the cleaning liquid, both cleaning the interior of the reaction vessel 51 and cleaning the wafers W can be achieved simultaneously. An ammonium chloride film is a film that may be possibly deposited. An ammonium chloride film may be deposited as a by-product of process, such as a silicon nitride film forming process that forms a silicon nitride film (Si₃N₄ film) through the interaction of a silane gas, such as a dichlorosilane gas, and ammonia gas.

In the foregoing embodiment, the wafers W held in a vertical position on the wafer boat 71 are subjected to the cleaning process and the thermal process. Therefore, the cleaning liquid adheres scarcely to the vertical surfaces by surface tension, the cleaning liquid drips off the wafers W by gravity and the cleaning liquid can be quickly removed from the surfaces of the wafers W to drain the cleaning liquid from the reaction vessel 51. Consequently, formation of water marks with the cleaning liquid, particularly with IPA, can be suppressed when the wafers W are dried by using nitrogen gas. The drying gas is not limited to nitrogen gas. For example, high-temperature, high-pressure, dry air having a low oxygen concentration may be used as the drying gas. The use of such dry air is more effective than nitrogen gas in suppressing the formation of water marks.

When the wafers W held in a vertical position are subjected to the thermal process, the spaces between the wafers W extend vertically in which the process gas flows from the bottom toward the top of the reaction vessel 51 and hence the process gas is able to flow smoothly upward through the spaces between the wafers W. Since the wafers W are held in a vertical position that facilitate the flow of the process gas in the reaction vessel 51, the surfaces of the wafers W can be uniformly exposed to the process gas. According to the present invention, wafers W may be processed by the thermal process in either a batch processing mode as mentioned above or a single-wafer processing mode. Although the effect available when wafers W are held in a vertical position, wafers W held in a horizontal position may be processed.

According to the present invention, the thermal processing apparatus does not need necessarily provided with a heater capable of heating the interior of the reaction vessel 51 at a high heating rate of 100° C./min as the heater 54. However, when the cleaning process and the thermal process are carried out in the same chamber, namely, the processing chamber in the heating furnace 5, it is desirable to keep a low temperature so that the cleaning liquid may not boil during the cleaning process and to keep a high temperature such as 1000° C., to promote the reaction of the process gas during the thermal process. Since the difference between those temperatures respectively for the cleaning process and the thermal process is large, the number of cycles of the thermal process can be increased and the throughput of the thermal processing apparatus can be increased by employing a high-capacity heater as the heater 54 to curtail time necessary for raising the temperature.

Moreover, since the present invention subjects the wafers to the thermal process after cleaning, an open wafer carrier may be used instead of the closed wafer carrier C. A wafer carrier C that holds wafers W in a vertical position may be used. 

1. A thermal processing apparatus for processing substrates by a predetermined thermal process that heats the substrates by a heating means, said thermal processing apparatus comprising: a reaction vessel provided with a drain port; a cleaning liquid supply means for supplying cleaning liquids into the reaction vessel to clean the substrates after the substrates have been loaded into the reaction vessel; and a process gas supply means for supplying a process gas into the reaction vessel to process the substrates by the thermal process after the cleaning liquids have been drained away from the reaction vessel.
 2. A thermal processing apparatus for processing substrates by a predetermined thermal process that heats the substrates by an external heating means, said thermal processing apparatus comprising: a reaction vessel provided with a drain port; a lid for closing an inlet opening of the reaction vessel; a substrate holding device mounted on the lid to hold the substrates; a carrying means for carrying the substrate holding device into and carrying the same out from the processing vessel; a cleaning liquid supply means for supplying cleaning liquids into the reaction vessel to clean the substrates after the substrate holding device holding the substrates has been loaded into the reaction vessel; and a process gas supply means for supplying a process gas into the reaction vessel to process the substrates by the thermal process after the cleaning liquids have been drained away through the drain port.
 3. The thermal processing apparatus according to claim 2, wherein the substrate holding device holds a plurality of substrates in a vertical position at horizontal intervals.
 4. The thermal processing apparatus according to claim 2, wherein the cleaning liquid supply means is connected to the lid.
 5. The thermal processing apparatus according to claim 2, wherein the drain port is formed in the lid.
 6. The thermal processing apparatus according to claim 1 or 2, wherein the cleaning liquid supply means is used for filling up the reaction vessel with the cleaning liquid, and the drain port is closed while the cleaning liquid is supplied into the reaction vessel.
 7. A thermal processing method comprising the steps of: carrying substrates into a reaction vessel; cleaning the substrates by supplying cleaning liquids into the reaction vessel; draining away the cleaning liquids from the reaction vessel; processing the substrates by a thermal process by supplying process gases into the reaction vessel and heating the interior of the reaction vessel after the cleaning liquids have been drained away.
 8. A thermal processing method that processes substrates by a predetermined thermal process in a reaction vessel by heating the substrates with an external heating means, said thermal processing method comprising the steps of: loading a substrate holding device with the substrates; loading the substrate holding device into the reaction vessel and hermetically closing an inlet opening of the reaction vessel by a lid; cleaning the substrate by supplying cleaning liquids into the reaction vessel; draining away the cleaning liquids from the reaction vessel; and processing the substrates by the thermal process by supplying a process gas into the reaction vessel and heating the interior of the reaction vessel.
 9. The thermal processing method according to claim 8, wherein the step of loading the substrate holding device with the substrates loads the substrates onto the substrate holding device such that the substrates are held in a vertical position at horizontal intervals.
 10. The thermal processing method according to claim 8, wherein the cleaning liquids are supplied through a discharge port formed in the lid into the reaction vessel.
 11. The thermal processing method according to claim 8, wherein the cleaning liquids are drained away through a drain port formed in the lid.
 12. The thermal processing method according to claim 7 or 8, wherein the step of supplying the cleaning liquids into the reaction vessel fills up the reaction vessel with the cleaning liquid. 